1. Field of the Invention
The present invention relates to a network lock method and a related apparatus, and more particularly, to a network lock method and a related apparatus by ciphered network lock and inerasable deciphering key.
2. Description of the Prior Art
In modern society, wireless communication networks have become one of the most important ways of communicating with people and exchanging information. Everyone can take advantage of the service of a wireless communication network easily and enjoy the power of accessing worldwide information anywhere and anytime via a convenient cell phone. For permanently maintaining the market and managing communication networks, it has become important to the information industry to improve the quality of communication services, maintain the communication order of communication networks, and ensure the rights of the subscribers of communication networks.
In general, service of wireless communication is provided by a service provider. Cell phone subscribers pay fees for rights of access to the communication service. To protect the rights of legal subscribers, when a cell phone user uses the communication service, the cell phone determines whether the user is a legal subscriber by a network lock determination mechanism. If the user is not a legal subscriber, the cell phone is restricted to access the communication network directly. Please refer to FIG. 1. FIG. 1 is a block diagram of a conventional communication network comprising communication devices 12 and 13, and a service provider 28. The cell phone 12 is taken for example to illustrate the communication device in a conventional communication system 10. There are a wireless signal transceiver module 14, a processor 16 controlling functions of cell phone 12, a data memory 20 (a non-volatile memory such as a flash memory), a subscriber identification module card (SIM card) 24 capable of identifying the subscriber, a microphone 18A capable of transforming acoustic waves to electronic signals, a speaker 18B, and a man machine interface (MMI) 21. The man machine interface 21 may comprise a keypad, a display, a vibrator, etc., so that the user of the cell phone 12 is able to control the cell phone 12 and monitor the operation of the cell phone 12 via the man machine interface 21. For the service provider 28, there is a base station 29 capable of providing communication service by transmitting and receiving wireless signals among cell phones. For instance, the acoustic waves of the users voice at the cell phone 12 are received and transformed into electronic signals by the microphone 18A, encoded appropriately by the processor 16, then modulated into radio frequency (RF) signals in the transceiver module 14 and wirelessly emitted to the base station 29. The base station 29 wirelessly transmits the signals received from the cell phone 12 to the cell phone 13, so that the user of the cell phone 13 is able to receive the message from the user of the cell phone 12. For the acoustic message transmitted by the cell phone 13 to the cell phone 12, the base station 29 receives it from the cell phone 13 and then wirelessly transmits it to the cell phone 12. The cell phone 12 receives the wireless signals at the transceiver module 14 and demodulates them to a base band signal, then decodes them appropriately with the processor 16 and transmits them to the speaker 18B to transform them into acoustic waves so that the user of the cell phone 12 can hear them. In this manner, the user of the cell phone 12 and the user of the cell phone 13 are able to communicate via the communication service provided by the service provider 28.
However, as mentioned, to protect the rights of legal subscribers, verification of the network lock is carried out automatically in the cell phone 12 to determine whether the user of the cell phone 12 is permitted to use the service of the communication network 10. Typically, there is a subscriber identification number 26 stored in the SIM card 24 in the cell phone 12 to represent the identification of the user of the cell phone 12. Generally speaking, the SIM card 24 is detachably connected to the cell phone 12. When a user proposes to use the service of the communication network 10 via the cell phone 12, he inserts the SIM card 24 to the cell phone 12 so that the cell phone 12 is able to identify the subscriber. Corresponding to the subscriber identification number 26 stored in the SIM card 24, there are a device identification number 23 and access information 22 of the verification procedure stored in the data memory 20. The device identification number 23 is a unique identification number of the cell phone (such as an IMEI, International Mobile Equipment Identity). In other words, the device identification numbers of different cell phones are different. Access information 22 is adapted to record the status of the network lock of the cell phone 12. The network lock is adapted for defining what subscriber identification numbers are permitted to utilize the service of the communication network 10. The status of the network lock of the cell phone 12 and the permitted subscriber identification numbers are stored in access information 22. For example, when values of some fields of the subscriber identification number 26 are within a predetermined range, the cell phone 12 accepts the subscriber identification number 26 as a legal subscriber identification number. The predetermined range is recorded in the access information 22. In the prior art, when the verification is carried out in the cell phone 12, the processor 16 loads and reads the access information 22 in the data memory 20, and determines whether the network lock of the cell phone 12 is turned on accordingly. If the status of the network lock is recorded as on in the access information 22, the processor 16 further checks whether the subscriber identification number 26 recorded in the SIM card 24 is among the legal subscriber identification numbers recorded in the access information 22. If the subscriber identification number 26 is recognized as a legal subscriber identification number, for example, as previously mentioned, the values of some fields of the subscriber identification number 26 are within the recorded predetermined range, the processor 16 determines the owner of the SIM card 24 is a legal subscriber of the communication network 10, and allows the cell phone 12 to proceed with following procedures so that the user of the cell phone 12, that is, the owner of the SIM card 24, is able to utilize the service of the communication network 10 via the cell phone 12. On the contrary, if the processor 16 finds the subscriber identification number 26 in the SIM card 24 is beyond the range of legal subscriber identification numbers recorded in the access information 22, the processor 16 determines the owner of the SIM card 24 is not a legal subscriber of the communication network 10, and prevents access by the cell phone 12 to the communication network 10. On the other hand, if the processor 16 finds the status of the network lock stored in the access information 22 is off when proceeding with the verification, the processor 16 does not check the subscriber identification number 26, but allows the owner of the SIM card 24 to utilize the service of the communication network 10 via the cell phone 12 directly.
To sum up, the network lock of the prior art determines whether the owner of the SIM card 24 is permitted to utilize the service of the communication network 10 via the cell phone 12 according to the access information 22 stored in the data memory 20. However, the conventional method carries the risk that the network lock be broken by illegal users. For example, when an illegal user wants to break the network lock of the cell phone 12, the illegal user can obtain the access information of another cell phone of which the network lock is turned off. Since the network lock is off in this cell phone, the status of the network lock is stored as off in the access information. Therefore, the access information can be utilized to break the network lock. For example, even when the network lock of the cell phone 12 is recorded as on in the access information 22, the illegal user can overwrite the original access information 22 with unsanctioned access information in the data memory 20, replacing the original access information 22 with the unsanctioned access information. When the cell phone 12 proceeds with the verification, it follows the unsanctioned access information and does not turn on the network lock, and hence the network lock of the cell phone 12 is broken. Even in the situation that the subscriber identification number 26 on the SIM card 24 is not a legal subscriber identification number, the owner of the SIM card 24 is able to access the service of the communication network 10 via the cell phone 12 illegally. For the convenience in maintenance and testing, there are predetermined maintenance junctions in the data memory 20 of the cell phone 12. Illegal users can take advantage of these predetermined maintenance junctions to write the breaking access information into the data memory 20 and overwrite the original access information 22 with a special data tool, such as JTAG tool, breaking the network lock of the cell phone 12. More seriously, illegal users can rewrite the access information 22 directly. For example, one can break the network lock of the cell phone 12 by rewriting the status of the network lock in the access information 22 to off. In addition, illegal users can delete the access information 22. Generally, in the cell phone 12 of the prior art, when the processor 16 finds that there is no access information in the data memory 20, the processor 16 proceeds with the network lock verification according to a predetermined access information, and the network lock usually is not turned on in this predetermined access information. Therefore, the network lock of the cell phone 12 is broken by the illegal users. Once the network lock is illegally broken, operations of the communication network 10 and the rights of the service provider and the legal subscribers (the owners of legal SIM cards) are affected.